JP3606472B2 - Pyrolytic boron nitride-coated multilayer molded body and method for producing the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a thermally decomposed boron nitride-coated multilayer molded article useful as a heater, electrostatic chuck, heat shield plate, heat shield cylinder, and heat absorbing band container having excellent heat resistance, corrosion resistance, and chemical stability, and a method for producing the same It is about.
[0002]
[Prior art]
Pyrolytic boron nitride (hereinafter abbreviated as PBN) has advantageous properties such as heat resistance, corrosion resistance, chemical stability, high purity, etc., and this is used as a pyrolytic graphite (PG) layer for ceramics such as Al ₂ O ₃ , Various applied products have been developed which are coated on a multilayer molded body formed on a substrate such as Si ₃ N ₄ , SiC, BN, PBN, etc. and take advantage of its characteristics. For example, in Japanese Patent Application No. 3-030393, a multi-layer heater in which a PG layer is formed on a PBN substrate is coated with a PBN layer, and in Japanese Patent Application Laid-Open No. 5-105557, an inner surface of a PBN container is applied. For example, a PG endothermic layer is formed and a PBN insulating protective coating layer is coated thereon.
[0003]
[Problems to be solved by the invention]
However, when the PBN layer is coated on the outermost surface of the multilayer molded body, there is a drawback that cracks, peeling, and the like are likely to occur in the PBN coating layer.
The present invention is a pyrolytic boron nitride-coated multilayer molded body in which such disadvantages are eliminated, and in particular, a PBN coating layer is formed on the surface of a multilayer molded body in which this molded body forms a graphite layer on a boron nitride substrate. An object of the present invention is to provide a PBN-coated multilayer molded article useful as a coated heater, electrostatic chuck, heat shield plate, heat shield cylinder, and heat absorption banded container, and a method for producing the same.
[0004]
[Means for Solving the Problems]
As a result of investigating the cause of cracks and peeling phenomenon in the PBN coating layer in order to solve such problems, the present inventors have found that internal stress is present at the corners of the PBN-coated multilayer molded body and the irregularities and edges of the surface. The present invention has been completed by ascertaining the concentration and studying this stress distribution method. That is,
A pyrolytic boron nitride-coated composite comprising a pyrolytic boron nitride layer formed on the surface of a multilayer molded article obtained by providing a graphite layer on a substrate made of boron nitride and removing a portion thereof to form a pattern. In the method for producing a layered molded product, when the irregular shape formed by removing the graphite layer is composed of a plurality of planes , the surface direction of the plane adjacent to the surface of the molded product is formed . A pyrolytic boron nitride-coated multilayer molded article characterized in that the angle formed with the lamination direction is in the range of 45 to 90 °, and a method for producing the same.
[0005]
Hereinafter, the present invention will be described in detail.
[Action]
As a result of investigating the cause of cracks and peeling phenomena occurring in the PBN coating layer, it was found that internal stress was concentrated on the surface of the end of the multilayer molded body and the concavo-convex part parallel to the substrate stacking direction. did.
The cause of the internal stress is due to the anisotropy of the thermal expansion coefficient of BN and PBN. The thermal expansion coefficient α _{c in} the stacking direction of the BN substrate is about 10 times the thermal expansion coefficient α _{a in the} direction perpendicular thereto. This is because the value is doubled. Therefore, as shown in FIG. 4, if the substrate surface is a plane perpendicular to the stacking direction (A portion in FIG. 4), the thermal expansion coefficients of the substrate and the covering coincide with α _a , but the substrate surface is parallel to the stacking direction. In part B, the coefficient of thermal expansion is α _c , and _a difference of 10 times from α _a occurs. Therefore, when the vertical surface of the groove cut for pattern processing in the cross section of the multilayer molded body has a difference in thermal expansion coefficient between the PBN coating layer and the multilayer molded body, when cooled from the PBN vapor deposition temperature to room temperature, In the meantime, stress is generated. Therefore, as shown in FIG. 1 (c) , as a stress reduction method, when the concave and convex shape on the surface of the molded body is a square groove composed of a plurality of planes, the plane adjacent to the surface of the molded body and the stacking direction of the substrate are formed. the angle theta, also as shown in FIG. 1 (e), in the case of semicircular grooves uneven shape composed of curved surfaces, the angle theta between the laminating direction of the tangent line and the base of the curved surface to 45 to 90 ° It was solved by. That is, the thermal expansion coefficient in the substrate surface direction and the thermal expansion coefficient of the coated PBN layer are made closer.
In general, α _c = 20 × 10 ^-6 / ° C and α _a = 2 × 10 ^-6 / ° C, where α _{c is} the coefficient of thermal expansion in the stacking direction of the BN substrate and α _a is the direction perpendicular thereto. It is done. When the angle between the arbitrary direction and the stacking direction is θ, the thermal expansion coefficient αθ in that direction is given by the following equation.
(1 + ΔTα (θ)) ² = (Cosθ (1 + ΔTα _c )) ² + (Sinθ (1 + ΔTα _a )) ² This relationship indicates that α (θ) is α _c when θ is 0 ° as shown in FIG. In the case of 90 °, α (θ) becomes α _a . When θ is 45 °, the difference between α (θ) and α _a is almost ½. That is, in the uneven shape on the surface of the substrate, as shown in FIGS. 1C and 1E, if the angle θ between the planar direction or the tangential direction of the curved surface and the stacking direction of the substrate is 45 to 90 °, The difference in coefficient of thermal expansion from the PBN layer coated on the surface becomes as small as 1/2 or less, the internal stress is greatly reduced, and peeling and cracking can be prevented.
[0006]
The greatest feature of the present invention is that the graphite layer on the surface of the multilayer molded body before the PBN coating layer is formed is cut in order to reduce the internal stress generated between the PBN coating layer and the multilayer molded body as much as possible. When processing, when the surface uneven shape is composed of a plurality of planes, the angle θ between the surface direction of the plane adjacent to the surface of the molded body and the stacking direction of the substrate, and when it is formed of a curved surface, the tangent line and the substrate The angle formed by the laminating direction is 45 to 90 °. If this is less than 45 °, a sufficient stress relaxation effect cannot be obtained, and cracks and peeling occur.
[0007]
The BN substrate of the present invention consists of a PBN compact by CVD or a BN sintered body by hot pressing, and the graphite layer is pyrolytic graphite (PG) or amorphous carbon by pyrolysis of an organic polymer substance. It is made up of.
Next, an example of a processing method for the ceramic heater will be described with reference to FIGS. 1 (a), (b), (c), (d), (e), and (f).
First, a graphite layer serving as a heating resistor is formed on the BN substrate 1 of FIG. 1A to a thickness of 50 to 100 μm by, for example, the CH ₄ CVD method (FIG. 1B), and the heater pattern is formed. Milling is performed to remove (FIG. 1 (c) when a trapezoidal end mill is used or (e) when a circular end mill is used). At this time, in the uneven surface shape , the angle θ between the surface direction (FIG. 1 (c)) or the tangential direction (FIG. 1 (e)) and the substrate stacking direction needs to be in the range of 45 to 90 °. It is. Next, a PBN coating layer 3 is formed thereon by CVD (FIG. 1 (d) or (f)) to complete the ceramic heater.
As the PBN-coated multilayer molded body produced by these methods, a good product without cracking or peeling was obtained.
[0008]
Hereinafter, although the embodiment of the present invention will be specifically described with reference to examples, the present invention is not limited thereto.
(Example)
In the example, a PBN substrate of 100 mmφ x 1.2 mmt was placed in a CVD apparatus, heated to 1900 ° C, high purity propane gas 5 SLM and hydrogen 20 SLM were introduced, maintained at 12.5 Torr, maintained at 1900 ° C, 7.5 hours Thus, a 50 μm PG deposited layer was obtained (FIG. 1B). Next, using a trapezoidal type and a circular type end mill, θ = 60 °, respectively, and a depth d = 300 μm (FIG. 1 (c) for a trapezoidal end mill, FIG. 2 (d) for a circular type end mill) Formed. Next, this was installed in a CVD apparatus, heated to 1800 ° C, BCl ₃ , NH ₃ , and H ₂ were introduced at 1 SLM, 5 SLM, and 20 SLM, respectively, held at 1800 ° C, and reacted at 8.7 Torr for 6 hours. A 50 μm thick PBN coating was obtained (FIGS. 1D and 1F). When these heaters were energized in a vacuum vessel and the temperature was lowered to 25 to 1000 ° C., no cracks or peeling occurred in 20 heat cycles.
[0009]
(Comparative example)
When the trapezoidal type and the circular type end mill are used, in Example 1 except that the heater pattern shown in FIG. 2 is formed by setting θ = 30 ° and cutting at a depth d = 300 μm in FIGS. Under the same conditions, PBN-coated heaters were produced. When these heaters were energized in a vacuum vessel and heated from 25 ° C. to 1000 ° C., the PBN coating was peeled off at the first time.
[0010]
【The invention's effect】
According to the present invention, a method for producing a pyrolytic boron nitride-coated multilayer molded body in which defects such as cracks and delamination caused by internal stress generated during film formation are eliminated, and the pyrolytic boron nitride-coated multilayer molding is provided. As a body, a ceramic heater, an electrostatic chuck, a heat shield plate, a heat shield cylinder or a container with a heat absorption band can be provided, and its utility value is extremely high in industry.
[Brief description of the drawings]
FIG. 1 is a process chart showing an example of a processing method of the present invention in a longitudinal sectional view.
(A) A BN substrate is shown.
(B) shows the formation of a graphite layer.
(C), (e) shows the formation of a heater pattern.
(D), (f) The formation of a PBN layer on a multilayer molded body is shown.
FIG. 2 is a top view showing an example of a heater pattern.
FIG. 3 is a graph showing the relationship between the angle θ between the surface direction of the concavo-convex surface formed by the concavo- convex shape on the surface of the multilayer molded body or the tangential direction of the curved surface and the stacking direction of the substrate and the thermal expansion coefficient α (θ).
FIG. 4 is a schematic diagram showing the relationship between thermal expansion coefficients α _a and α _c at each interface of a PBN-coated multilayer molded body.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 BN base | substrate 2 Graphite layer 3 PBN coating layer 5 Attachment, conductive terminal hole (theta) The angle formed by the tangential direction of a surface direction or a curved surface, and the lamination direction of a base | substrate

Claims (2)

A pyrolytic boron nitride-coated composite comprising a pyrolytic boron nitride layer formed on the surface of a multilayer molded article obtained by providing a graphite layer on a substrate made of boron nitride and removing a part of the graphite layer to form a pattern. In the method for producing a layered molded body, when the uneven shape formed by removing the graphite layer is composed of a plurality of planes , the surface direction of the plane adjacent to the surface of the molded body is formed . A method for producing a pyrolytic boron nitride-coated multilayer molded article, wherein an angle formed with a lamination direction is in a range of 45 to 90 °. The pyrolytic boron nitride-coated multilayer molded body obtained by using the production method according to claim 1 is any one of a heater, an electrostatic chuck, a heat shield plate, a heat shield cylinder, or a container with a heat absorption band. A pyrolytic boron nitride-coated multilayer molded article.

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